1. Field of the Invention
The present invention relates to a joined body, particularly relates to a high pressure discharge lamp using a ceramic discharge tube.
2. Description of the Related Art
A high pressure discharge lamp has a ceramic discharge tube with two end portions, in which sealing members (usually referred to as a ceramic plug) are inserted, respectively, to seal the respective end portions. A through hole is formed in each sealing member and a metal member, to which a predetermined electrode system is attached, is inserted within the through hole. An ionizable light-emitting material is introduced and sealed within the inner space of the discharge tube. Known high pressure discharge lamps include a high pressure sodium vapor and metal halide lamps, the latter exhibiting more superior color coordination. The lamp may be used in high temperature condition by forming the discharge tube by a ceramic material.
In such discharge lamp, it is necessary to air-tightly seal between the end portion of the ceramic discharge tube and a member for supporting an electrode system. The ceramic discharge tube has a main body with a shape of a tube with two narrow ends, or a barrel, or a straight tube. The ceramic discharge tube is made of, for example, alumina sintered body.
The specification of Japanese patent application No. 178,415/1999 (EPO EP0982278, A1) discloses the following structure. The joining portion between the end portion of a ceramic discharge tube and a member for supporting an electrode system comprises main phase contacting the discharge tube, and an intermediate ceramic layer contacting the supporting member and existing between the supporting member and the main phase. The main phase is composed of a porous bone structure, with open pores and made of a sintered product of metal powder, and ceramic phase impregnated into the open pores in said porous bone structure. Herewith, such joined structure has improved air-tightness and resistance to corrosion, and repeated thermal cycles does not result in the fracture of the joined structure.
The inventor further examined the above sealing structure and, therefore, achieved a joined structure having resistance to fatigue and fracture, even when the structure is subjected to repeated thermal cycles between a high temperature, for example 1000xc2x0 C. or higher, and room temperature.
That is, it is an object of the invention to provide a joined structure having resistance to fatigue and fracture, even when the structure is subjected to repeated thermal cycles between a high temperature, for example 1000xc2x0 C. or higher, and room temperature.
It is another object of the invention to apply such joined structure to a high pressure discharge lamp, for improving the resistance to a corrosive gas, such as a metal halide, and the air-tightness and for avoiding the fracture of the joined structure due to repeated cycles of turning-ons and turning-offs.
The present invention provides a joined body of a first member made of a metal and a second member made of a ceramic or a cermet. The joined body comprises a joining portion interposed between the first member and the second member for joining the first and second members, wherein the joining portion comprises main phase contacting the first member and an intermediate ceramic composition layer contacting the second member and existing between the second member and the main phase. The main phase is composed of a porous bone structure, made of a sintered product of metal powder and with open pores, and ceramic composition layer impregnated into the open pores in the porous bone structure. Each of the intermediate ceramic composition layer and said impregnated ceramic composition layer has a crystallinity of more than 50%.
The present invention further provides a ceramic discharge lamp comprising: a ceramic discharge tube with an inner space formed therein and end portions, the inner space being filled with an ionizable light-emitting material and a starter gas and an opening being formed within the end portion; an electrode system provided within the inner space; a sealing member with a through hole formed therein, a part of the sealing member being fixed within the opening of the ceramic discharge tube; and a metal member; wherein the metal member and the sealing member constitute the above air-tight joined body. The metal member is the first member and the sealing member is the second member.
The present invention further provides a ceramic discharge lamp comprising: a ceramic discharge tube with an inner space formed therein and end portions, the inner space being filled with an ionizable light-emitting material and a starter gas and an opening being formed within the end portion; an electrode system provided within the inner space; and a metal member; wherein the metal member and the ceramic discharge tube constitute the above air-tight joined body. The metal member is the first member and the ceramic discharge tube is the second member.
The present invention provides a joined structure of a first member made of a metal, such as molybdenum, and a second member made of a ceramic or a cermet, in which the members may be joined with a high strength, the joined structure has improved air-tightness and resistance to corrosion, and repeated thermal cycles do not result in the fracture of the joined structure. The invention provides a method for manufacturing the same.